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Effects of convection and solid wall on the diffusion in microscale convection flows
Zhang J(张俊); Fan J(樊菁); Fei F(费飞); Fan J(樊菁)
Source PublicationPhysics of Fluids
2010-12-21
Volume22Issue:12Pages:122005
ISSN1070-6631
AbstractThe diffusive transport properties in microscale convection flows are studied by using the direct simulation Monte Carlo method. The effective diffusion coefficient D is computed from the mean square displacements of simulated molecules based on the Einstein diffusion equation D = x2 t /2t. Two typical convection flows, namely, thermal creep convection and Rayleigh– Bénard convection, are investigated. The thermal creep convection in our simulation is in the noncontinuum regime, with the characteristic scale of the vortex varying from 1 to 100 molecular mean free paths. The diffusion is shown to be enhanced only when the vortex scale exceeds a certain critical value, while the diffusion is reduced when the vortex scale is less than the critical value. The reason for phenomenon of diffusion reduction in the noncontinuum regime is that the reduction effect due to solid wall is dominant while the enhancement effect due to convection is negligible. A molecule will lose its memory of macroscopic velocity when it collides with the walls, and thus molecules are hard to diffuse away if they are confined between very close walls. The Rayleigh– Bénard convection in our simulation is in the continuum regime, with the characteristic length of 1000 molecular mean free paths. Under such condition, the effect of solid wall on diffusion is negligible. The diffusion enhancement due to convection is shown to scale as the square root of the Péclet number in the steady convection regime, which is in agreement with previous theoretical and experimental results. In the oscillation convection regime, the diffusion is more strongly enhanced because the molecules can easily advect from one roll to its neighbor due to an oscillation mechanism. © 2010 American Institute of Physics. doi:10.1063/1.3528310
Subject Area流体力学
DOI10.1063/1.3528310
URL查看原文
Indexed BySCI
Language英语
WOS IDWOS:000285770200010
WOS KeywordRAYLEIGH-BENARD CONVECTION ; MOLECULAR-DYNAMICS ; THERMAL CREEP ; RAREFIED-GAS ; PASSIVE TRANSPORT ; HYDRODYNAMICS ; ATTRACTORS ; SIMULATION ; SYSTEM
WOS Research AreaMechanics ; Physics
WOS SubjectMechanics ; Physics, Fluids & Plasmas
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Cited Times:11[WOS]   [WOS Record]     [Related Records in WOS]
Document Type期刊论文
Identifierhttp://dspace.imech.ac.cn/handle/311007/43261
Collection高温气体动力学国家重点实验室
Corresponding AuthorFan J(樊菁)
Recommended Citation
GB/T 7714
Zhang J,Fan J,Fei F,et al. Effects of convection and solid wall on the diffusion in microscale convection flows[J]. Physics of Fluids,2010,22(12):122005.
APA Zhang J,Fan J,Fei F,&樊菁.(2010).Effects of convection and solid wall on the diffusion in microscale convection flows.Physics of Fluids,22(12),122005.
MLA Zhang J,et al."Effects of convection and solid wall on the diffusion in microscale convection flows".Physics of Fluids 22.12(2010):122005.
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